Abstract Sonars and echosounders are widely used for remote sensing of life in the marine environment. There is an ongoing need to make the acoustic identification of marine species more correct and objective and thereby reduce the uncertainty of acoustic abundance estimates. In our work, data from multi-frequency echosounders working simultaneously with nearly identical and overlapping acoustic beams are processed stepwise in a modular sequence to improve data, detect schools and categorize acoustic targets by means of the Large Scale Survey System software (LSSS). Categorization is based on the use of an acoustic feature library whose main components are the relative frequency responses. The results of the categorization are translated into acoustic abundance of species. The method is tested on acoustic data from the Barents Sea, the Norwegian Sea and the North Sea, where the target species were capelin ( Mallotus villosus L.), Atlantic mackerel ( Scomber scombrus L.) and sandeel ( Ammodytes marinus L.), respectively. Manual categorization showed a high conformity with automatic categorization for all surveys, especially for schools.

Abstract An experimental deployment of a new type of unmanned vessel is presented. The Christian Michelsen Research SailBuoy, a remotely-controlled surface vehicle, sampled near-surface properties during a two-month mission in the northern Gulf of Mexico in March–May, 2013. Averaged over the entire deployment, the vessel speed over ground was 42 ± 30 cm s − 1 ( ± one standard deviation) with a maximum of 180 cm s − 1 . During the 62 days of the mission, the SailBuoy covered a total range of appr...more

A combination of scientific, economic, technological and policy drivers is behind a recent upsurge in the use of marine autonomous systems (and accompanying miniaturized sensors) for environmental mapping and monitoring. Increased spatial–temporal resolution and coverage of data, at reduced cost, is particularly vital for effective spatial management of highly dynamic and heterogeneous shelf environments. This proof-of-concept study involves integration of a novel combination of sensors onto buo...more

In the fall of 2009 a 3-frequency (38, 123, and 210 kHz) upward-looking echo sounder was deployed in 95m of water at the inshore Folger Passage node of the NEPTUNE Canada observatory. NEPTUNE (North-East Pacific Time-Series Undersea Networked Experiments) is an 800 km cabled ocean observation system off the Pacific coast of Canada which is now online and operational. The system supplies DC power to permanently sited instruments, and supports a bi-directional high-bandwidth datastream using optic...more

Johnsen, E., Pedersen, R., and Ona, E. 2009. Size-dependent frequency response of sandeel schools. - ICES Journal of Marine Science, 66: 1100-1105.Annual Norwegian sandeel surveys have been conducted in the North Sea since 2005 to measure the stock of lesser sandeel (Ammodytes marinus). Target identification is often a major challenge in acoustic surveys, and discriminant analyses have been used to separate echoes accurately from schools of herring, mackerel, and sandeel based on their acoustic-...more

Acoustic surveys are used to estimate the abundance and distribution of many fish species, and have been based traditionally on data collected at a single acoustic frequency. Although it has been known for some time that the use of additional frequencies can provide information on the nature of the acoustic target, the knowledge and technology required to combine the so-called "multifrequency data" in an appropriate manner has been limited. The use of several transducers of different frequencies...more

Abstract Broadband echosounder systems provide very high range resolution that could resolve different parts of fish and hence provide estimates of fish size. The potential for, and accuracy of, direct acoustic sizing of fish was tested on fish-like targets of known dimensions and orientations. Prolate spheroids, 91–477 mm long, with and without an air-filled inclusion (simulating a fish swim-bladder), made from polyvinyl-alcohol-cryogel, were suspended in an acoustic beam and rotated while the ...more

Abstract A method to estimate the mean standard length ( L ¯ ) of juvenile salmon in aggregations using multi-frequency (67 and 125 kHz) acoustic analysis was developed. An autonomous, single beam echosounder (Acoustic Zooplankton and Fish Profiler (AZFP), ASL Environmental Sciences) was deployed on the seafloor in Okisollo Channel, British Columbia during peak juvenile salmon migration season in 2015 and 2016. A positive correlation was found between the difference in the mean volume backscatte...more

Abstract Acoustic scattering layers (SL) at various depths are common phenomena in most oceans, but the organisms that make up these layers vary and so does their density, and hence the backscattered energy. During two crossings of the deep Fram Strait between the shelves at Svalbard and Northeast Greenland at latitudes 77°N and 79°N, we registered epipelagic and mesopelagic SL across the entire Fram Strait and quantified their acoustic backscattered energy. In addition, one pelagic trawl haul w...more

Biomass of the schooling fish Rastrineobola argentea (dagaa) is presently estimated in Lake Victoria by acoustic survey following the simple 'rule' that dagaa is the source of most echo energy returned from the top third of the water column. Dagaa have however been caught in the bottom two-thirds, and other species occur towards the surface: a more robust discrimination technique is required. We explored the utility of a school-based random forest (RF) classifier applied to 120 kHz data from a l...more

Abstract Distribution of micronekton was investigated during early summer of 2013, using data from a cruise covering the central parts of four north Atlantic basins, the Norwegian Sea (NS), Iceland Sea (ICS), Irminger Sea (IRS), and Labrador Sea (LS). Continuous underway acoustics mapped vertical and horizontal distributions, and trawl sampling provided data on biomass and taxonomic composition. The hull mounted acoustics and trawl catches suggested that, among the four basins, biomass of epipel...more

Advancing our understanding of ocean biogeochemistry, biology, and ecosystems relies on the ability to make observations both in the ocean and at the critical boundaries between the ocean and other earth systems at relevant spatial and temporal scales. After decades of advancement in ocean observing technologies, one of the key remaining challenges is how to cost-effectively make measurements at the increased resolution necessary for illuminating complex system processes and rapidly evolving cha...more